Yes, I agree with SPG. There's really no need to force the issue, is there? I think that's one of the good things about homeschooling: you can go fast in some areas and slow in others as it suits your child. I would think that *extremely short* but frequent practice sessions--maybe several per day--might be your best bet.
You might even want to focus on pre-writing exercises. Tracing circles and lines and things like that rather than "real" writing might be more helpful.
I'm certainly not an OT, but if he's struggling as much as you describe and getting that upset with it, it doesn't seem like it's very useful to him. He doesn't sound ready for what he's trying to do. Less seems like it might be more for him.
